In this study, a new method for producing Si, called ''halidothermic reduction'', was investigated with the purpose of producing solar-grade silicon (SOG-Si); by this method, SiCl 4 was reduced by gaseous subhalide used as the reductant. Si was produced by reacting SiCl 4 with Al subhalides, which were produced by reacting AlCl 3 with metallic Al. Fibrous Si with diameters ranging from submicrons to several tens of micrometers was deposited as a result of halidothermic reduction of SiCl 4 by an Al subchloride (AlCl x ) reductant at 1273 K. The size of Si deposits and the reaction rate were increased by simultaneously supplying AlCl 3 and SiCl 4 vapors to a reaction tube holding Al metal. The impurity level of the obtained Si was found to be lower than the detection limit of X-ray fluorescence. Halidothermic reduction is suitable for producing high-purity Si since all reactants and byproducts exist in the vapor phase. Further, this process has high productivity since the overall reaction is a highly scalable metallothermic reduction reaction.